In winter or on a rainy day, frost is formed on a glass surface of a vehicle because of a temperature difference outside and inside of the vehicle. In addition, in the case of an indoor ski resort, a dew condensation phenomenon occurs because of a temperature difference inside where there is a slope and outside of the slope. In order to solve this, a heating glass has been developed. The heating glass uses a concept where after attaching a hot line sheet onto the glass surface or directly forming a hot line on the glass surface, electricity is applied to both terminals of the hot line to generate heat from the hot line, thereby increasing the temperature of the glass surface.
In order to manufacture the heating glass, a transparent conductive layer is required. A type of transparent conductive layer includes a layer formed by using a transparent conductive material such as indium tin oxide (ITO) or a film formed by forming a metal thin film using a metal material such as Ag which is an opaque conductive material and forming a transparent insulating material around the metal thin film. Further, a transparent conductive layer may be formed such that a metal material which is an opaque material is patterned to increase an opening ratio, thereby increasing transmittance and a line width of a metal pattern is limited to 30 micrometer or less to limit recognition of the pattern.
When the transparent conductive layer formed by the above-mentioned methods is used, the transparent conductive layer may serve as a heating element and also blocks an electromagnetic wave due to high conductivity. Currently, various electronic apparatuses using an electromagnetic wave through a front glass of a vehicle are used. For example, a device for automatically collecting a toll on the highway or a GPS for a navigation system performs communication using an electromagnetic wave. Further, electromagnetic communication is performed through the glass of the vehicle in order to use a mobile phone. The above-mentioned transparent conductive layer has a problem that lowers a communication reception rate for communication using the above-mentioned electromagnetic wave.
In order to solve the above-mentioned problem, methods are suggested to remove a transparent conductive layer at a part of the glass of the vehicle, specifically, portion where a rear view mirror is attached to be used as a communication window. When a heating performance is applied to the front glass of the vehicle, bus bars which connect the heating element with a power supplying unit are mainly provided at a top portion and a bottom portion of the glass of the vehicle. In this case, when the transparent conductive layer is removed from the communication window zone, a distance between the bus bars provided at the top portion and the bottom portion of a region where the communication window is provided is inevitably shorter than a distance between bus bars of the other zones and thus electric current which flows in the heating element is concentrated, so that heat is nonuniformly generated.
In order to solve the problems, a method which forms transparent heating elements which have different conductivity in each area and a method which uses two or more bus bars (U.S. Pat. No. 6,734,396) are suggested. However, the above methods may cause the increase of manufacturing cost, so that the above methods are not easy to be commercially adopted.